Comparison of polymorphism in Golang and polymorphism in Java

For object-oriented, we can easily say its three characteristics: encapsulation, inheritance, polymorphism.
Today I will record the comparison between golang and java polymorphism in the learning process.

一、 Golang

在golang中，多态主要是通过接口实现的。
可以按照同一的接口来调用不同的实现，这时接口变量就呈现不同的形态
并且相对于java，少了extends和implements关键字

for example

//声明一个Usb接口
type Usb interface {
	//接口内声明了两个没有实现的方法
	Start()
	Stop()
}

type Phone struct {
	Name string
}

//让Phone实现Usb接口的方法
func (p Phone) Start() {
	fmt.Println("手机插入，开始工作...")
}
func (p Phone) Stop() {
	fmt.Println("手机拔出，停止工作...")
}

type Camera struct {
	Name string
}

//让Camera实现Usb接口的方法
func (ca Camera) Start() {
	fmt.Println("相机插入，开始工作...")
}
func (ca Camera) Stop() {
	fmt.Println("相机拔出，停止工作")
}

There are two ways to interface polymorphism:

Polymorphic parameter

//编写电脑的Working方法,接收一个Usb接口类型变量
//只要是实现了Usb接口  (所谓实现了Usb接口  就是指实现了Usb接口的所有声明的方法)
func (computer Computer) Working(usb Usb) { //usb接口变量就体现出多态的特点 usb Usb称为多态参数
	usb.Start()
	usb.Stop()
}

func main(){
    computer := Computer{}
    phone := Phone{}
    camera := Camera{}
    //关键点  传入实现接口的类型
    computer.Working(phone)
    computer.Working(camera)
}

Polymorphic array

func main() {

	//使用多态数组
	usbArr := [...]Usb{
		Phone{"华为Mate 30 Pro"},
		Phone{"小米10 Pro 至尊版"},
		Camera{"索尼"},
	}

	fmt.Println(usbArr)

	var computer Computer

	for _, value := range usbArr {
		computer.Working(value)
		//传入的是哪个类型，就是哪个类型实现了多态
	}

}

Second, Java

#java中多态体现的格式:
父类类型 变量名 = new 子类对象
变量名.方法名()
#父类类型:指子类对象继承的父类类型，或者实现的父接口类型

When calling a method in a polymorphic way, first check whether the method exists in the parent class, if not, a compilation error will occur; if there is, the method that is rewritten by the subclass will be executed. Simply denoted as:Compile and look at the left (parent class), execute and look at the right (subclass)

for example

public abstract class Animal {
    //抽象方法，继承该类的子类需要重写
    public abstract void eat();
}

public class Dog extends Animal{
    @Override
    public void eat() {
        System.out.println("狗吃肉");
    }

    public void watchHouse(){
        System.out.println("狗看家");
    }
}

public class Cat extends Animal{
    @Override
    public void eat() {
        System.out.println("猫吃鱼");
    }

    public void catchMouse(){
        System.out.println("猫抓老鼠");
    }
}

public class Test {
    public static void main(String[] args) {
        Animal a = new Cat(); 
        Animal a2 = new Dog();

        a.eat(); //猫吃鱼  
        a2.eat(); //狗吃肉

        //向下转型 为了防止转型失败 使用instanceof判断类型
        if (a instanceof Cat){
            Cat cat = (Cat)a;
            cat.catchMouse();
        }else if(a instanceof Dog) {
            Dog dog = (Dog)a2;
            dog.watchHouse();
        }
    }
}